In the packet-switched domain in the UMTS (Universal Mobile Telecommunications System) standardized as a third generation mobile communication system, a UMTS bearer service (PDP (Packet Data Protocol) context) is specified as a bearer service model. The “PDP context” indicates information on settings of a logical path configuration used when user IP packets are transferred in the UMTS network. An address of a mobile terminal (UE) is called a PDP address. To access an IP network, the UE uses one of such one or more IP addresses respectively assigned by one or more GGSNs (Gateway GPRS Support Nodes), each of which is a node for connection from the mobile communication network to an external IP network.
Each GGSN is identified by an APN (Access Point Name). In the UMTS, each UE is assigned one or more PDP addresses (IP addresses assigned to a UE when PDP contexts are configured), and multiple PDP contexts can be simultaneously set up for each pair of an PDP address and an APN. In the case of setting up multiple PDP contexts, different GTP (GPRS Tunneling Protocol) tunnels can be related to the respective PDP contexts. Each GTP tunnel is assigned a tunnel endpoint identifier (TEID) serving as its identifier, and each UMTS bearer can be identified based on the TEID. The UE can connect to the external IP network by using these UMTS bearers (see Non-patent Documents 1 and 2).
Meanwhile, in the LTE (Long Term Evolution) & SAE (System Architecture Evolution) standardized as a next generation mobile communication system, an SAE bearer service is specified as in the UMTS, and a logical path configuration is set up by using PDP contexts in a similar manner. Standardization of the LTE & SAE is now being advanced so as to enable multiple bearers to be logically set up as in the UMTS by setting up a default bearer when a UE attaches to a mobile communication network, and by setting up a dedicated bearer in response to a request after the default bearer is set up. In addition, the above standardization is being advanced to enable exchange of information on the above settings at the time of a handover between the UMTS and the LTE & SAE (see Non-patent Document 3).
In addition, in the UMTS and next generation mobile communication systems, specified is a service model based on multiple service domain/external IP networks (PDNs) for allowing connection to the multiple PDNs that provide services. In the service model, it is defined that, to get services provided by the PDNs, a UE is connected to those multiple PDNs via Packet Data Network Gateways (PDN GWs), each of which is a gateway device between the corresponding PDN and a mobile network, and is assigned different PDP addresses (IP addresses assigned to a UE) by the respective PDN GWs (see Non-patent Documents 4 and 5).    [Non-patent Document 1] TS 24.008 Mobile radio interface Layer 3 specification; Core network protocols; Stage 3    [Non-patent Document 2] TS 23.060 General Packet Radio Service (GPRS); Service description; Stage 2    [Non-patent Document 3] TR 23.882 3GPP system architecture evolution (SAE): Report on technical options and conclusions    [Non-patent Document 4] TS 23.401 3GPP System Architecture Evolution:GPRS enhancements for LTE access    [Non-patent Document 5] TS 23.402 3GPP System Architecture Evolution:Architecture Enhancements for non-3GPP accesses